What is the typical scapulohumeral rhythm during arm elevation?

• A. For every 1 degree of glenohumeral abduction, the scapula rotates 2 degrees
• B. For every 2 degrees of glenohumeral abduction, the scapula rotates about 1 degree
• C. Scapula does not rotate during arm elevation
• D. Scapula rotation equals glenohumeral abduction degree

Answer: (B)

During arm elevation the scapulothoracic joint and the glenohumeral joint move together in a coordinated pattern called scapulohumeral rhythm. The typical relationship is 2 parts of glenohumeral abduction for every 1 part of scapular upward rotation. In practical terms, about 120 degrees of humeral (glenohumeral) abduction and about 60 degrees of upward scapular rotation combine to produce roughly 180 degrees of arm elevation. This means the scapula rotates about 1 degree for every 2 degrees of glenohumeral abduction, which is the best description of the rhythm.

This rhythm reflects how the scapula helps maintain the correct alignment of the shoulder socket and prevents impingement while allowing the arm to raise smoothly. The other ideas—scapula not rotating, rotation being equal to glenohumeral movement, or scapula rotating more than the humerus—don't match the natural 2:1 pattern observed during typical arm elevation.